Method of imparting corrosion resistance to zirconium base alloys



Dec. 27, 1966 /o IMPROVEMENT IN THE I4-DAY WEIGHT GAIN BY COLD WORK O.BERTEA ETAL 3,294,594 METHOD OF IMPARTING CORROSION RESISTANCE TO ZIRGONIUM BASE ALLOYS Filed Nov. 8, 1965 EFFECT OF COLUMBIUM CONTENT ON THE IMPROVEMENT IN CORROSION THROUGH COLD REDUCTIONIMACHININGI' FURNA(E COOL ANNE AL 5O AIR COOL 'ANNEAL 20 ZIRCALOY-Z COLUMBIUM CONTENT OCTAVIAN BERTEA JAMES R. GROSS STANLEY R. S EAG LE INVENTORS United States Patent 3,294,594 METHOD OF ARTING CORROSION RESIST- ANCE T0 ZIRCONIUM BASE ALLOYS Octavian Bertea and Stanley R. Seagle, Warren, Ohio, and

James R. Gross, Kokomo, IntL, assignors to National Distillers and Chemical Corporation, New York, N.Y.-,

a corporation of Virginia Filed Nov. 8, 1963, Ser. No. 322,438 7 Claims. (Cl. 148-115) This application is a continuation-in-part of Serial No. 75,931, filed December 15, 1960, now abandoned.

The invention relates to zirconium base alloys and more particularly to a method or procedure for treating zirconium base alloys having low resistance to corrosion to impart substantially increased corrosion resistance to such alloys.

There. is an existing and unsatisfied need for wrought zirconium base alloy products having a combination of high strength and high corrosion resistance for the fabrication of equipment used in nuclear reactor devices such as nuclear steam generator power plant equipment.

One commercial zirconium alloy containing 1.5% tin, 0.10% chromium, 0.05% nickel, 0.12% iron, and a maximum of 60 ppm. nitrogen, sometimes known as Zircaloy-Z, has been used somewhat extensively because of its low corrosion rate at elevated temperatures when in the presence of water or steam. The corrosion rate of this alloy, that is, its weight gain during corrosion, is about 37 mg./dm. in 750 F.-1500 p.s.i.g. steam for 14 days, as compared with a corrosion rate for unalloyed zirconium under the same test conditions of about. 31 mg./dm. However, the strength of Zircaloy-2 at elevated temperatures (18,000 psi. yield strength at 900 F.) leaves much to be desired.

The unsatisfied need for wrought zirconium base alloy products requires a minimum 35,000 psi yield strength at 0.2% oifset at 900 F. with 10% minimum room temperature tensile elongation in 2 inches, not possessed by Zircaloy-2, combined with a corrosion rate comparable to that of Zircaloy-Z; or requires wrought zirconium base alloy products having at least 50% greater strengths than the strengths of Zircaloy-Z at all temperatures accompanied by a comparable corrosion rate.

A number of zirconium base alloys have been developed which satisfy the indicated high strength requirements, but each has a much higher corrosion rate or a much poorer corrosion resistance than required to satisfy the need.

The usual practice for making say A" hot rolled zirconium base alloy bars involves annealing hot rolled bars and then shot-blasting, pickling and straightening the bars. Similarly, hot rolled zirconium base alloy sheet, plate and strip products are usually hot rolled, then annealed and air cooled, then sand-blasted and pickled. Cold rolled zirconium base alloy sheet material normally is fabricated from hot rolled sheets produced in the manner described, the hot rolled sheets then being cold rolled to finished gauge, scrubbed, annealed, sand-blasted, pickled, slit to width, cut to finished length, leveled, inspected, tested and shipped.

All of the indicated procedures thus involve a usual pickling operation as a final metal treatment step following any annealing treatment.

In searching for wrought zirconium base alloy products combining high corrosion resistance and high strength at various temperatures and particularly at elevated temperatures, we observed that a peculiar film was present on the surfaces of some of the wrought products after the described final pickling operation in the manufacture of hot rolled bar and sheet products and cold rolled sheet products, when normal pickling solutions were used.

Patented Dec. 27, 1966 Although later established to be incorrect, initially it was believed that this peculiar film present on the surfaces of the finished products was the cause of the high corrosion rate characterizing wrought zirconium base alloy products investigated that had strengths high enough to satisfy. the existing need.

We then unexpectedly discovered that the intolerable high corrosion rate of the investigated zirconium base alloys that did have the required high strengths could be reduced to a corrosion rate low enough to satisfy the requirements by introducing cold work into the material. Cold work as defined and as used throughout this specification and claims, means the permanent strain produced by an external force in a metal below its recrystallization temperature. Several examples of cold working operations are cold extrusion, machining, cold rolling, drawing, coining, shot blasting, peening,.rocking and grinding. The terms machined and machining mean to plane, shape, turn, mill, etc., by a machine or machines.

Further investigation established that when material having a high or unacceptable corrosion rate, and which was treated by the indicated final cold working operation to reduce the corrosion rate to a low acceptable value, was again treated to remove the effect of cold working as by a stress relief treatment, the corrosion rate again increased to an unacceptable high value. This established that. it was critical to use a cold working operation as a final treatment operation to achieve the low corrosion rate characteristic.

Further investigation established that it is not the presence of the peculiar film following pickling which caused the high corrosion rate. Pickled cold work strip was found to have an appreciably lower corrosion rate than pickled strip without cold work, thus indicating the necessity for cold work in the final product.

We have been unable to account for the reason why the introduction or retention of cold .work in producing high strength wrought zirconium base alloy products imparts high corrosion resistance or a low corrosion rate to such products. This result is completely. contrary to the belief and teachings in the art of manufacture and treatment of metals and alloys. The literature on corrosion resistance of metals and alloys abounds with statements that cold work stimulates or increases corrosion of the cold Worked surfaces. There is no known information in any literature, prior to our discovery, that a final cold working step in the manufacture of wrought zirconium base alloy products can be used to increase appreciably the corrosion resistance of such products.

We have made a further discovery that the zirconium base alloys which exhibit decreased corrosion when treated in accordance with the invention by a final cold working operation, are characterized by reduced H pickup as corrosion progresses. This characteristic is of great importance because nuclear reactor applications for zirconium base alloy materials require as little H pickup as possible.

Accordingly, it is an object of the present invention to provide a new method of imparting high corrosion resistance to zirconium base alloys which normally have low corrosion resistance or are characterized by a high corrosion rate.

Furthermore, it is an object of the present invention to provide a new method of making wrought zirconium base alloy products having strengths at all temperatures at least 50% greater than the strengths at the same temperatures of Zircaloy-Z, to impart to such products a corrosion rate comparable to the 37 mg./dm. corrosion rate in 750 F.-1500 p.s.i.g. steam for 14 days, of Zircaloy-Z.

Also, it is an object of the present invention to process the high strength zirconium base alloy in such a manner that cold work is retained in the final wrought product, thus achieving improved corrosion resistance.

Also, it is an object of the present invention to provide a particular series of steps or mode of treatment used in the manufacture of wrought zirconium base alloy products which reduces the rate of H pickup as corrosion progresses.

Moreover, it is an object of the present invention to provide for the manufacture of zirconium base alloy products having a desirable and heretofore unobtained combination of high strength and high corrosion resistance.

Finally, it is an object of the present invention to provide new method of treating zirconium base alloy products in the manufacture thereof for obtaining the foregoing desider-ata, and which overcomes existing difficulties and problems and satisfies an existing need in the art.

These and other objects and advantages, apparent to those skilled in the art from the following description and claims, may be obtained, the stated results achieved, and the described difficulties overcome, by the methods, steps, procedures and treatments which comprise the present invention, the nature of which is set forth belowillustrative of the best modes in which we have contemplated applying the principles-and which are particularly and distinctly pointed out and set forth in the appended claims forming part hereof.

The critical discovery of the invention is that a cold 4 Working operation is used to impart low corrosion rate characteristics to the investigated wrought zirconium base alloy products which have high strengths at all temperatures, but which normally exhibit an intolerable and unacceptable high corrosion rate.

In accordance with the invention, Zirconium base alloy material which has high strength at both room and various elevated temperatures is melted and hot rolled in accordance With usual or standard practice for producing bar, plate, sheet or strip products. The hot rolled or hot worked material is then annealed in the usual manner and a cold working operation following annealing is performed to impart a low corrosion rate characteristic to the product.

In the case of cold rolled sheet or strip material, hot rolling may be performed in the usual manner followed by annealing and pickling of the hot rolled material. Then the pickled hot rolled material, in accordance with the invention, is cold rolled to desired gauge in order to impart the low corrosion rate characteristics to the material.

The results of carrying out the treatment of the invention are illustrated in Table I below, for a number of columbium containing zirconium base alloys and Zircaloy- 2. The colu-mbium content varies from in Zircaloy-2 to 20% in DM 1374. In general, the alloys of this invention will contain about 1 to 20% by weight of columbium. It will be understood, however, that the amount columbium employed need only be sufficient to achieve the desired high strength properties.

TABLE I.IHE EFFECT OF FINAL METAL TREATMENT ON THE WEIGHT GAIN OF SEVERAL COLUMBIUM CONTAINING ZIRCONIUM BASE ALLOYS AFTER A 14-DAY EXPOSURE TO 750 F. STEAM Weight Gain, Percent Final Metal Treatment Step mg./dm. in Improvement Heat N 0. Alloy Constituents Heat Treatment or Steps 14 Days at Thru Cold 750 F., 1,500 Work p.s.i.g. Steam DM 1383 Zr-1% Sn-1% Cir-1% Cb 1,500 F.-1 hr.-FC Machined and pickled 51.9 +29.8

Machined 36. 4 DM 1384 Zr-3% Sll-3% (Jr-1% Cb 1.550 F.1 hr.-FC Machined and pickled 101. 9 +22.

Machined 78. 9 1,550 F.-1 hr.-AC Machined and pickled 87.8 +13. 2

Machined 76. 2 X-2315 Zr-2% Sn -2% (Jr-2% Cb 1,475 F.1 hr.-FC Machined and pickled 119. 8 +46. 4

Machined 64. 1 1,475 F.1 lir.-AC Machined and pickled 78.0 +26. 3

Machined 57. 5 X-2407 Zr-2% Sn-2% (Jr-2.5% Cb 1,500" F.% hr.-FC Machined and p1ckled 69. 1 +44. 3

Machine 38. 5 1,500 F.% hr.-AC Machined and p1ckled. 69. 1 +266 Mac 'ne 50. 7 X-2406 Zr-1% Sn-1% (Jr-2.5% Ob l,500 F.% hr.-FO %gac1l; ined and p1ckled 6 +63. 7

ac 1n 1,506 F.% hr.-AC Machined and pickled 62. 2 +39. 3

Machine 37. 4 1,500 F.% hr.-WQ, Machined and pickled 121. 3 +57. 4

Machined 51. 7 X-2404 Zr-3% Sn-1% (Jr-2.5% Cb 1,500 FHA hr.-FC Machined and p1ckled 126. 6 +64. 8

Machine 44. 5 1,500 F.-% hr.-AO Machlned and p1ckled 76. 5 +54. 8

Machined 43. 2 1,500 F.% hr.-WQ Machined and pickled 184. 4 +60. 2

Machined 73. 3 X-2279 Zr-1% Sn-3% CIT-3% Cb 1,525 F.1hr.-FO Machined and pickled 131. 6 +64. 3

Machined 47. 0 1,525" F.1 hr.-AC Machined and pickled 87. 3 +45. 5

Machined 47. 6 X-2280 Zr-8% Sn-1% Ci -3% Cb 1,425 F.1 hr.-FC Machined and pickled 168. 5 +75. 2

Machined 41. 8 1,425 F.1 lir.-AO Machined and picklecL. 109. 3 +58. 8

Machine 45. 0 X-2405 Zr-3% Sn-1% (Jr-3% Cb 1,500 F.% Ill-F0 Machined and pickled 139. 4 +55. 0

Machine 62. 7 l,500 F.% hr.-AC Machined and 137. 7 +71. I

MachinecL 39. 8 1,500 F.% hlZ-WQ, Machined a 185. 3 +57. 6

Machined. 7S. 5 DM 1271 Zr-0.3% Sn-1% (Jr-3% Cb 1,425 F.1l1r.FO Machined a 163.0 +70. 1

- Machined 48. 8

1,425 F.1 Ina-AG 'Machined and pickled 82. 5 +45. 6

Machined 44. 9 Zr-0.3% Sn-l% Ci -5% Cb 1,100 F.96 hrs.-FO--- Hot Roll and pickle 103. 6 +51. 8

Hot Roll, pickle, cold roll 50. 0 Zr-0.3% S11-1% (Jr-% Cb 1,100 F.96 hrs-F0 Hot Roll and pickle 110. 1 +36. 4

Hot Roll, pickle, rold roll 70.0 Zr-0.3% Sn-1% (Jr-15% Cb 1,100 F.96 hrs-F0 Hot Roll and pickle 118. 5 +40. 4

i Hot Roll, pickle, cold rolL- 70. 6 Zr-0.3% Sn-1% Ci Cb 1,100 F.96 hrs.-I C Hot Roll and pickle 126. 9 +31. 5

Hot Roll, pickle, cold roll 87. 0 Zircaloy-Z 1,550 F.% hr.-AC Machined and pickled 37. 0 9. 2

Machined 40. 4

Specimens of all the compositions in Table I with less than 5% Cb were annealed accomplished by an air cool or a furnace cool. The specimen in the first line for each heat treatment was machined and then pickled, while the specimen in the second line for each heat treatment was machined as a final cold working operation after annealing. The same amount of machining was perlformed for each specimen either as a final cold Working operation or prior to pickling so that the results can be compared, and the machining in the above and in all of the specific embodiments was accomplished by planing, unless otherwise indicated.

in the first line for each heat containing 5% Ob or :greater, the specimens were hot rolled and pickled. 1n the second line for each heat, the specimens were treated in the same manner but Were cold rolled to gauge following the pickling operation.

Of the twenty-seven examples of columbium containing zirconium base alloys, all except one showed a significant improvement by cold working. The improvement in one case (X2280) was as great as 75%, while Zircaloy-2 showed a minus 9.2%.

The percent improvement that can be expected in the 14-day weight gain is dependent on the columbium content and heat treatment. This is illustrated in the accompanying figure, where data from Table I of zirconium base alloys containing 3% or less columbium content were used. The data for zirconium alloys containing 5% or greater columbium were not used, since the improvement in corrosion resistance was obtained by a different cold working process. The graft shows that for both heat treatments the percent improvement becomes greater as the colum-bium content is increased. For a constant columbium content, specimens furnace cooled .from the annealing temperautre showed a greater percentage improvement by cold working than air cooled specimens. However, the improvement noted in air cooled specimens was still appreciable.

The data in Table I show that zirconium :base alloys investigated which normally have a high corrosion rate 6: may be treated in accordance with the invention to impart high corrosion resistance to the material.

Table I illustrated the efiect of cold work on the corrosion resistance of zirconium base alloys containing up to 20% Cb. The cold Work was obtained by machining. During machining, the depth of cold work is very shallow and can be removed by a pickle operation. The percent of cold deformation is not certain. Table II illustrates, in more quantitative manner, the effect of cold work on the corrosion rate. In these examples, the cold work was obtained by cold rolling. The reductions studied were up to 88%. The corrosion tests were carried out for extended times so that accurate corrosion rates could be established. These results clearly show that the corrosion rate is progressively decreased as the amount of cold work (as measured by cold reduction) is increased.

Also included in the table are results for machined specimens. The post transition corrosion rate would indicate that the cold work introduced during machining is equivalent to the amount of cold work that is obtained in a reduction by cold rolling.

As illustrated in Table I, the cold work introduced during machining is superficial and can easily be removed by a pickle. During cold rolling, the cold work is distributed throughout the cross section with the greatest amount being at the surface and progressively decreasing away from the surface. Therefore, a pickle of a cold rolled product should not completely erase the beneficial effects of the cold working operating since the sunface after pickling would have some cold work remaining. Table III illustrates-the effect of pickling a cold rolled surface. For example, the Zr-2.5% Cb-1% Cr.-3% Sn alloy without cold work has a post transition corrosion rate of 4.1 mg./ dm. day. By cold rolling 88%, this rate is decreased to 2.0. Pickling the cold Worked specimen does not raise the rate to the original value but to an intermediate value of 2.7. Thus, the pickle removed a highly cold worked surface exposing a new surface which contains slightly less cold work. This example and others in Table HI show that the cold work in the material and not the lack of peculiar pickle film is the critical feature of the invention.

TABLE IL-EFFECT OF GOLD WORKING ON THE CORROSION RESISTANCE 0F Cb CONTAINING ZIRCONIUM BASE ALLOYS Weight Gain, mg./dm. in Indicated Time at 750 F.,

1,500 p.s.i.g., Steam Post Tran- Alloy Composition Source of Cold Work 1 sition Corrosion Rate 14 28 56 84 112 140 168 mg./d1n. /Day Days Days Days Days Days Days Days Zr-2.5% Cb None 54 68 100 147 196 245 293 1. 7 4% Red. by cold rolling 51 63 101 i 143 182 222 260 1. 5 17% Red. by cold rolling 48 91 133 177 216 252 1. 4 50% Red. by cold rolling" 38 49 88 118 155 188 213 1. 1 38 49 67 100 124 142 166 0. 8 Machined all over 37 46 88 119 148 1. 0 Zr-2.5% Oil-1% Cr-1% Sn None 68 112 192 272 357 435 505 2. 9 6% Red. by cold rolling 68 105 194 279 370 449 526 3.0 16% Red. by cold rollin 54 88 159 238 315 388 457 2. S 60% Red. by cold rolling 40 72 133 192 253 313 368 2.1 87% Red. by cold rolling 35 56 97 142 185 230 273 1.6 Machined all over. 35 63 122 215 297 3. 1 Zr-2.5% (lb-1%, (Jr-3% Sn None 82 138 258 381 722 4.1 7% Red. by cold rolling. 73 128 255 368 491 597 697 4.1 16% Red. by cold rolling 63 122 244 361 492 600 4. 1 52% Red. by cold rolling 53 99 195 299 406 506 596 3. 5 88% Red. 'by cold rolling 37 46 88 142 200 254 318 2. 0 Machined all over 40 187 303 411 508 .1 3. 6 Zt-3.U% Chi-1%, Cr3% 5Y1 None a- 114 6% Red. by cold rolling 101 17% Red. by cold rolling 97 152 281 396 4. 3 50% Red. by cold rolling 47 174 270 3.2 88% Red. by cold rolling 38 47 79 242 304 2.0 Machined all over 41 56 132 220 320 .t 3. 3

1 Vacuum annealed at 1,450 F.2 hrs. and Furnace Cooled prior to cold working.

TABLE III.-THE EFFECT OF SURFACE REMOVAL ON THE CORROSION RESISTANCE OF GOLD WORKED COLUMBIUM CONTAINING ZIROONIUM BASE ALLOYS Weight Gain After Post Transition Alloy Composition Surface Condition 168 days in 750 F., Corrosion Rate,

1,500 p.s.i.g. Steam, mgJdInfl/day mgJdrn.

Zr-2.5% Cb Cold worked 293 l. 7 Cold worked 88% 166 0. 8 Gold worked 88% and ck 174 0. 9 Zr-2.5% Cb-1% Or-1% Sn Cold worked 0% 505 2.9 Cold worked 87% 271 1. 6 Cold worked 87% and pickle 306 1. 8 Zr-2.5% Clo-1% Cr-3% sn Cold worked 0% 722 4.1 Cold worked 38% 318 2. 0 Cold worked 88% and picklc 434 2. 7 Zr-3.0% Cb-l% (Jr-3% Sn Cold worked 88% 304 2.0 Cold worked 88% and pickle 418 2. 7

An additional experiment was conducted to establish TABLE VI the criticality of the cold work. The result of eliminating the effect of thefinal cold working operation of the pres- 20 Rm 02% ent invention is shown in Table IV, below, which lists at N0 Co po q 011900? corrosion test values for material from Heat No. X-228O (Zr-3% Snl% Cr-3% Cb) with the specimens machined D 4. Z -3 -1 b 13. 33, 000 and pickled 1n the first line, machmed 1n the second line M 138 1 2 1000 d um annealin Zr-0.37 Sn-lV (Jr-3'7 Cb. 1 12. 33,000 and mach ned and then sub ecte to a vacu g ZHW; SIPWZ CF39; Chm l 17 0 42' 000 OPCIEIEIOD 111 the thlfd 11116. DM 1375 Z 5% Cb 2 13,0 2 ,000 DM 1377--.- Zr-10% Cb 2 11.0 42, 000 DM 1375 Zr-l5% Cb 2 6. 5 48, 000 DM 1374.-.- Zr-% Cb 2 9. 5 53, 000 TABLE W 28128 Zircaloy-Z 23.0 18,000

750 F., 1,500 p.s.i.g. Steam 1 Percent Elongation i 1"- 2 Percent Elongation in 2". Specimen Preparation 3 27 35, The room temperature elongations of the alloys in Table VI, except DM 1375, satisfy the minimum room temperature elongation requirements indicated above. All Machined and ickled 168. 5 258. 4 Machinedunf 41.8 55. 9 of the heats have at least 50% greater yield strength ggi? (11,409: hr-mvacuum 138 3 225 4 at 900 F. than the 18,000 p.s.i. yield strength of Zircaloy-2, meeting the alternate strength requirements speci- The data in Table IV show that when the effect of a cold working operation was removed by annealing the cold worked material (third line), the corrosion is again increased from the low 41.8 Ing./drn. value to the uncorrosion when cold work is present, the hydrogen pickup is less. In this example, the hydrogen pickup during corrosion for a 0.1" thick specimen with no cold work would be 122 ppm. Through the introduction of cold work this has been reduced to 79 ppm. for an 80% cold reduction.

Room temperature elongation and yield strength at 900 F. values are given in Table VI, below, for several of the alloys evaluated in Table I. The last line of Table VI and presents values for Zircaloy-2.

fied above.

Referring to both Tables I and IV, treatment in accordance with the invention may be used to obtain wrought zirconium base alloy products which have high corrosion resistance combined with high strength as compared with the high corrosion resistance-low strength properties of Zircaloy-Z. Such a combination of properties has not, to our knowledge, ever been achieved in wrought zirconium base alloy products.

Accordingly, the new method of imparting corrosion resistance to zirconium base alloys of the present invention provides for the treatment of zirconium base alloys which may have high strength but low corrosion resistance to impart substantially increased corrosion resistance to such alloys comparable to that of Zircaloy-Z; provides a reduced rate of H pickup for high strength zirconium base alloys which have been treated to obtain increased corrosion resistance; and provides a new pro cedure solving a problem and eliminating difficulties existing in the art which may be carried out economically to produce wrought zirconium base alloy products having a heretofore unobtained combination of high strength and high corrosion resistance.

In the foregoing description, certain terms have been used for brevity, clearness and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are used for descriptive purposes herein, and not for the purpose of limitation, and are intended to be broadly construed.

Having now described the invention, the features, disco veries and principles thereof, the combined characteristics imparted to wrought zirconium base alloy products treated in accordance with the invention, and the new and useful results obtained, the new and useful methods, steps, procedures, treatments, discoveries and principles, and reasonable mechanical equivalents thereof obvious 9 to those skilled in the art, are set forth in the appended claims.

What is claimed is:

1. The method of increasing the corrosion resistance, as evidenced by decreasing the weight gain at least 13.2% when exposed to 750 F.1500 p.s.i.g. steam for 15 days, of wrought zirconium base alloy products containing about 1 to 20 weight .percent columbium having elevated temperature yield strengths at 900 F. between 28,000 and 53,000 p.s.i., which comprises the steps of hot working and annealing the alloy and finally cold working the surface of the alloy.

2. The method of claim 1 wherein said alloy is pickled after annealing but prior to cold working.

3. The method of claim 1 wherein the cold working is machining.

4. The method of claim 1 wherein the cold working is cold rolling.

5. The method of imparting high corrosion resistance of from 41.8 to 87 mg./dm. when exposed to 750 F. 1500 p.s.i.g. steam for 14 days to wrought zirconium base alloys containing about 1 to 20 weight percent columbium having from 28,000 p.s.i. to 53,000 p.s.i. yield strength at 900 F. and corrosion resistance of 87.3 to 168.5 mg./dm. when exposed to 750 F.1500

p.s.i.g. steam for 14 days when produced -by hot rolling, annealing and pickling, including the steps of hot rolling the alloy to develop the 28,000 psi. to 53,000 p.s.i. yield strength at 900 F., annealing the hot rolled alloy, and cold working the surface of the alloy.

6. The method of claim 5 wherein the cold working is machining.

7. The method of claim 5 wherein the cold working is cold rolling.

References Cited by the Examiner UNITED STATES PATENTS 2,772,964 12/1956 Thomas et a1. -177 OTHER REFERENCES AECU3561: Scaling of Zirconium and Zirconium Alloys, August 1957, Burke et al., pp. 913 relied on.

Journal of Metals, September 1955, pp. 1034-1041, Zirconium-Columbium Diagram, Rogers et a1.

DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, Examiner.

H. F. SAITO, Assistant Examiner. 

1. THE METHOD OF INCREASING THE CORROSION RESISTANCE, AS EVIDENCED BY DECREASING THE WEIGHT GAIN AT LEAST 13.2% WHEN EXPOSED TO 750*F-150 P.S.G. STEAM FOR 15 DAYS, OF WROUGHT ZIRCONIUM BASE ALLOY PRODUCTS CONTAINING ABOUT 1 TO 20 WEIGHT PERCENT COLUMBIUM HAVING ELEVATED TEMPERATURE YIELD STRENGTHS AT 900*F. BETWEEN 28,000 AND 53,000 P.S.I., WHICH COMPRISES THE STEPS OF HOT WORKING AND ANNEALING THE ALLOY AND FINALLY COLD WORKING THE SURFACE OF THE ALLOY. 